Curable-on-demand polysiloxane coating composition

ABSTRACT

A curable composition comprises (a) at least one polydiorganosiloxane, fluorinated polydiorganosiloxane, or combination thereof comprising reactive silane functionality comprising at least two hydroxysilyl moieties; (b) at least one polydiorganosiloxane, fluorinated polydiorganosiloxane, or combination thereof comprising reactive silane functionality comprising at least two hydrosilyl moieties; and (c) at least one photoactivatable composition that, upon exposure to radiation, generates at least one base selected from amidines, guanidines, phosphazenes, proazaphosphatranes, and combinations thereof; wherein at least one of the components (a) and (b) has an average reactive silane functionality of at least three.

STATEMENT OF PRIORITY

This application claims the priorities of U.S. Provisional ApplicationsNos. 61/360,068, filed Jun. 30, 2010; and 61/360,007, also filed Jun.30, 2010; the contents of which are hereby incorporated by reference.

FIELD

This invention relates to curable coating compositions comprisingreactive silane functionality and, in other aspects, to processes forcoating the compositions and articles prepared thereby.

BACKGROUND

Moisture-curable polysiloxane compositions cure in the presence ofmoisture to form crosslinked materials such as release coatings andsurface treatments that are useful in many industries. For example, apolysiloxane or fluorinated polysiloxane is often selected to providemoisture-curable release coatings suitable for use withpressure-sensitive adhesives. The moisture for curing is typicallyobtained from the atmosphere or from a substrate to which thecomposition has been applied, although it can also be added to thecomposition (for example, to enable curing in depth or in confinement).

Moisture-curable polysiloxane compositions usually comprise siloxanepolymers having groups (for example, alkoxysilyl or acyloxysilylmoieties) that can react in the presence of moisture to form cured (thatis, crosslinked) materials. Moisture-curable compositions comprisingalkoxysilyl or acyloxysilyl functionality typically cure in tworeactions. In the first reaction, the alkoxysilyl or acyloxysilyl groupshydrolyze in the presence of moisture and a catalyst to form silanolcompounds having hydroxysilyl groups. In the second reaction, thehydroxysilyl groups condense with other hydroxysilyl, alkoxysilyl, oracyloxysilyl groups in the presence of a catalyst to form—Si—O—Si—linkages. The two reactions occur essentially simultaneouslyupon generation of the silanol compound. Commonly used catalysts for thetwo reactions include Bronsted and Lewis acids. A single material cancatalyze both reactions.

Preferably, the hydrolysis and condensation reactions proceed quicklyafter the moisture-curable composition has been applied, for example, toa substrate. At the same time, however, the reactions must not occurprematurely, for example, during processing or storage.

A good balance between these properties is often difficult to obtain, asrapid reactivity and storage stability are opposite properties to eachother. For example, highly active catalysts such as tetraalkyl titanateesters rapidly accelerate the moisture-curing reaction but, at the sametime, can make it difficult to process the materials without riskingpremature gelation in feed tanks, coating equipment, and othermanufacturing and handling apparatus. Control of the amount of moisturecan be critical, with too little moisture potentially resulting in slowor incomplete cure and too much moisture resulting in premature cure.

A variety of approaches have been used for providing moisture-curablecompositions that have acceptable cure rates without processing andstorage difficulties. For example, two-part systems have been developed(one part comprising a functional siloxane polymer and the other partcomprising a catalyst), with the two parts being mixed immediately priorto use. While this approach has been useful in small-scale applications,it has been less efficient for large-scale manufacturing, where delayscaused by having to mix the two parts have been undesirable.Furthermore, coating operations must be completed expeditiously beforethe composition cures in the pot, and this has been difficult whenworking with large surface area substrates or a large volume ofcomposition.

Ammonium salt catalysts have been developed that are inactive untilheated sufficiently to liberate an acid compound that initiates themoisture curing reaction. Liberation of the acid also generates anamine, however, that must be removed by evaporation. In addition, theheat used to activate the catalyst can damage heat-sensitive substratesonto which the composition has been applied.

Other materials (for example, onium salts such as sulfonium and iodoniumsalts) have been used to generate acid species in situ upon irradiation(for example, irradiation with ultraviolet light). Such materials havenot required heat activation and therefore have enabled the use ofheat-sensitive substrates without damage (and without the production ofundesirable species requiring removal), but the materials have beenrelatively expensive, have required moisture control, and have exhibitedcure inhibition on some substrates.

Conventional tin catalysts such as dibutyl tin dilaurate can providestable curable polysiloxane compositions that can be processed andcoated without premature gelation. In addition to typicalmoisture-curable systems, it has been found that curable compositionscomprising dual reactive silane functionality in the form of hydrosilyland hydroxysilyl groups (dehydrogenatively-curable systems) can be curedby using tin catalysts. The compositions have been widely used forpressure-sensitive adhesive and mold release applications but havesometimes suffered from relatively short pot lives. In addition, the useof tin catalysts is becoming particularly problematic because theorganotin compounds generally employed as catalysts are now consideredto be toxicologically objectionable.

Acceleration of cure has been achieved by the use of compounds such assubstituted guanidines, diorganosulfoxides, imidazoles, amidines, andamines in combination with tin catalysts in room temperature vulcanizingsilicone compositions. Amine compounds including amidines have also beenproposed for use in the absence of tin catalysts for curingmoisture-curable, silyl-functional organic polymers, but practicalcurability of alkoxysilyl-functional organic polymers and acceptableadhesion to substrates were achieved only with strongly basic amines(those exhibiting a pH of at least 13.4 in aqueous solution).

SUMMARY

Thus, we recognize that there exists an ongoing need for curablepolysiloxane compositions that can provide acceptable cure rates withoutsignificant processing and storage difficulties (for example, due topremature gelation). Preferably, these compositions will be efficientlyprocessable (for example, without the need for mixing of a two-partsystem prior to cure), will employ catalysts that do not generatespecies requiring removal, and/or will not require heat activation (soas to enable curing at relatively low temperatures and/or the use ofheat-sensitive substrates). The compositions preferably will employcatalysts that are relatively non-toxic, provide compositions that arerelatively stable in solution but relatively fast-curing upon drying,effective in relatively low concentrations, and/or effective underrelatively low (or no) moisture conditions. Ideally, the compositionswill be curable on demand (for example, by generation of the catalyst insitu) and coatable without the need for significant addition of solvent(for example, in 100 percent solids form).

Briefly, in one aspect, this invention provides a curable polysiloxanecomposition comprising dual reactive silane functionality. Thecomposition comprises

-   -   (a) at least one polydiorganosiloxane, fluorinated        polydiorganosiloxane, or combination thereof comprising reactive        silane functionality comprising at least two hydroxysilyl        moieties (that is, monovalent moieties comprising a hydroxyl        group bonded directly to a silicon atom);    -   (b) at least one polydiorganosiloxane, fluorinated        polydiorganosiloxane, or combination thereof comprising reactive        silane functionality comprising at least two hydrosilyl moieties        (that is, monovalent moieties comprising a hydrogen atom bonded        directly to a silicon atom); and    -   (c) at least one photoactivatable composition that, upon        exposure to radiation, generates at least one base selected from        amidines, guanidines, phosphazenes, proazaphosphatranes, and        combinations thereof;        wherein at least one of components (a) and (b) has an average        reactive silane functionality of at least three (that is,        component (a) has at least three hydroxysilyl moieties (on        average), component (b) has at least three hydrosilyl moieties        (on average), or both). Components (a) and (b) preferably        comprise at least one polydiorganosiloxane (more preferably, at        least one polydialkylsiloxane; most preferably, at least one        polydimethylsiloxane). Preferably, component (a) is        hydroxyl-endblocked, so as to comprise two terminal hydroxysilyl        moieties (on average).

The photoactivatable composition preferably comprises at least one1,3-diamine compound that is substituted on at least one nitrogen atomby at least one aralkyl radical. The base that is generated uponexposure of the photoactivatable composition to radiation preferablycomprises at least one amidine (most preferably,1,8-diazabicyclo[5.4.0]-7-undecene (DBU)).

It has been discovered that, unlike standard amine bases such as4,4′-trimethylenebis(1-methylpiperidine) (which are ineffective), theabove-described bases can effectively catalyze the curing (apparently,by condensation) of polysiloxane compositions comprising reactive silanefunctionality in the form of hydrosilyl and hydroxysilyl moieties. Ithas been further discovered that photoactivatable compositions can beeffectively used to generate the bases in situ. This in situ generationhas been found to provide curable-on-demand polysiloxane compositionsthat can exhibit enhanced storage stability and/or pot life and that canbe coated in completely solvent-free (that is, 100 percent solids) orsubstantially solvent-free (using only a relatively small amount ofsolvent) form.

Upon photoactivation, the curable polysiloxane compositions can curerelatively rapidly (for example, upon irradiation curing can occurwithin periods of time as short as seconds or less) even at temperaturesas low as ambient (for example, about 23° C.), without the need for heatactivation, and the photoactivatable compositions can be effective inrelatively small amounts (for example, at concentrations as low as about0.5 weight percent or less, based upon the total weight of components(a), (b), and (c)). Thus, curable polysiloxane compositions comprisingthe photoactivatable compositions can be suitable for use in high speedcoating and curing operations in an industrial setting, without the needfor addition of heat. In spite of such effective curability, the curablepolysiloxane compositions can exhibit relatively good storage stability(for example, for a period of weeks or more in a closed container)and/or relatively long pot life (for example, on the order of days inthe absence of light) in 100 percent solids form or, optionally, in avariety of solvents (for example, heptane, methyl ethyl ketone, or acombination thereof), without the need for mixing of a two-part systemimmediately prior to use.

In surprising contrast with prior art compositions, the insitu-generated bases can be effective in the curable polysiloxanecomposition of the invention in the substantial absence of othercondensation catalysts and/or in the substantial absence of moisture.The bases can be used as substitutes for conventional tin catalysts toprovide organometallic catalyst-free, curable polysiloxane compositions,without the need for changes in the nature of the polysiloxanecomponents of conventional tin-cured polysiloxane compositions (forexample, release coating compositions such as Syl-Off™ 292 coatingcomposition, available from Dow Corning Corporation, Midland, Mich.).Unlike the conventional tin catalysts, at least some of the bases (forexample, DBU) and their photoactivatable precursors are relativelynon-toxic and therefore suitable for use in preparing relativelyenvironmentally friendly or “green” polysiloxane compositions.

The curable polysiloxane composition of the invention can be cured toprovide crosslinked networks having properties that can be tailored tothe requirements of various different applications (for example, byvarying the natures, relative amounts, and/or degrees of reactive silanefunctionality of starting components (a) and/or (b)). Thus, the curablepolysiloxane composition can be used to provide coatings having avariety of surface properties for use in numerous coating applications(for example, use as release coatings for pressure-sensitive adhesives,protective coatings, water- and/or oil-repellent coatings or surfacetreatments, and the like). The curable polysiloxane composition of theinvention can be particularly useful in relatively sensitiveapplications requiring careful and/or tailored control of surfaceproperties (for example, release coating applications), as the basecatalysts and their photoactivatable precursors do not appear to producespecies requiring removal and, in some embodiments, are sufficientlyvolatile to be evaporated from the composition during processing,thereby leaving essentially no catalyst contamination in the curedmaterial (in contrast with the metal contamination of conventional tincatalysts, which can be particularly problematic in the area ofelectronics).

In view of the foregoing, at least some embodiments of the curablepolysiloxane composition of the invention meet the above-described,ongoing need for curable-on-demand, solvent-free compositions that canprovide acceptable (or even exceptional) cure rates without significantprocessing and storage difficulties (for example, without the need formixing of a two-part system prior to cure, for contaminant removal,and/or for heat activation). At least some embodiments of the curablepolysiloxane composition also employ catalysts and catalyst precursorsthat are relatively non-toxic, while being effective in relatively lowconcentrations and/or under relatively low (or no) moisture conditions.

In another aspect, this invention also provides a coating processcomprising

(a) providing the above-described curable polysiloxane composition ofthe invention;

(b) providing at least one substrate having at least one major surface;

(c) applying the curable polysiloxane composition to at least a portionof at least one major surface of the substrate; and

(d) inducing the curable polysiloxane composition to cure to form acoating by exposing at least a portion of the curable polysiloxanecomposition to radiation.

In yet another aspect, this invention provides an article comprising atleast one substrate having at least one major surface, the substratebearing, on at least a portion of at least one major surface, a coatingprepared by the above-described coating process.

DETAILED DESCRIPTION

In the following detailed description, various sets of numerical ranges(for example, of the number of carbon atoms in a particular moiety, ofthe amount of a particular component, or the like) are described, and,within each set, any lower limit of a range can be paired with any upperlimit of a range. Such numerical ranges also are meant to include allnumbers subsumed within the range (for example, 1 to 5 includes 1, 1.5,2, 2.75, 3, 3.80, 4, 5, and so forth).

As used herein, the term “and/or” means one or all of the listedelements or a combination of any two or more of the listed elements.

The words “preferred” and “preferably” refer to embodiments of theinvention that may afford certain benefits under certain circumstances.Other embodiments may also be preferred, however, under the same orother circumstances. Furthermore, the recitation of one or morepreferred embodiments does not imply that other embodiments are notuseful, and is not intended to exclude other embodiments from the scopeof the invention.

The term “comprises” and variations thereof do not have a limitingmeaning where these terms appear in the description and claims.

As used herein, “a,” “an,” “the,” “at least one,” and “one or more” areused interchangeably.

The above “Summary of the Invention” section is not intended to describeevery embodiment or every implementation of the invention. The detaileddescription that follows more particularly describes illustrativeembodiments. Throughout the detailed description, guidance is providedthrough lists of examples, which examples can be used in variouscombinations. In each instance, a recited list serves only as arepresentative group and should not be interpreted as being an exclusivelist.

Definitions

As used in this patent application:

“catenated heteroatom” means an atom other than carbon (for example,oxygen, nitrogen, or sulfur) that replaces one or more carbon atoms in acarbon chain (for example, so as to form a carbon-heteroatom-carbonchain or a carbon-heteroatom-heteroatom-carbon chain);

“cure” means conversion to a crosslinked polymer network (for example,through catalysis);

“fluoro-” (for example, in reference to a group or moiety, such as inthe case of “fluoroalkylene” or “fluoroalkyl” or “fluorocarbon”) or“fluorinated” means only partially fluorinated such that there is atleast one carbon-bonded hydrogen atom;

“fluorochemical” means fluorinated or perfluorinated;

“heteroorganic” means an organic group or moiety (for example, an alkylor alkylene group) containing at least one heteroatom (preferably, atleast one catenated heteroatom);

“hydrosilyl” refers to a monovalent moiety or group comprising a siliconatom directly bonded to a hydrogen atom (for example, the hydrosilylmoiety can be of formula —Si(R)_(3-p)(H)_(p), where p is an integer of1, 2, or 3 and R is a hydrolyzable or non-hydrolyzable group(preferably, non-hydrolyzable) such as alkyl or aryl);

“hydroxysilyl” refers to a monovalent moiety or group comprising asilicon atom directly bonded to a hydroxyl group (for example, thehydroxysilyl moiety can be of formula —Si(R)_(3-p)(OH)_(p) where p is aninteger of 1, 2, or 3 and R is a hydrolyzable or non-hydrolyzable group(preferably, non-hydrolyzable) such as alkyl or aryl);

“isocyanato” means a monovalent group or moiety of formula —NCO;

“mercapto” means a monovalent group or moiety of formula —SH;

“oligomer” means a molecule that comprises at least two repeat units andthat has a molecular weight less than its entanglement molecular weight;such a molecule, unlike a polymer, exhibits a significant change inproperties upon the removal or addition of a single repeat unit;

“oxy” means a divalent group or moiety of formula —O—; and

“perfluoro-” (for example, in reference to a group or moiety, such as inthe case of “perfluoroalkylene” or “perfluoroalkyl” or“perfluorocarbon”) or “perfluorinated” means completely fluorinated suchthat, except as may be otherwise indicated, there are no carbon-bondedhydrogen atoms replaceable with fluorine.

Component (a)

Polysiloxanes suitable for use as component (a) of the curablepolysiloxane composition of the invention include polydiorganosiloxanes,fluorinated polydiorganosiloxanes, and combinations thereof (preferably,polydiorganosiloxanes) comprising reactive silane functionalitycomprising at least two hydroxysilyl moieties (that is, monovalentmoieties comprising a hydroxyl group bonded directly to a silicon atom).The polysiloxanes can be oligomers, polymers, or a combination thereof.Preferably, the polysiloxanes are polymers, which can be linear,branched, or cyclic. Useful polymers include those that have random,alternating, block, or graft structures, or a combination thereof.

The molecular weight and the reactive silane functionality of component(a) (including the number and nature of the hydroxysilyl moieties) ofthe polysiloxanes can vary widely, depending upon, for example, themolecular weight and the reactive silane functionality of component (b)and the properties desired for the curable and/or cured composition. Atleast one of components (a) and (b) has an average reactive silanefunctionality of at least three, however (that is, component (a) has atleast three hydroxysilyl moieties (on average), component (b) has atleast three hydrosilyl moieties (on average), or both), so as to enablethe formation of a crosslinked network.

Preferably, the polydiorganosiloxanes, fluorinatedpolydiorganosiloxanes, and combinations thereof used for component (a)are hydroxyl-endblocked, so as to comprise two terminal hydroxysilylmoieties (on average). The polysiloxanes preferably have a weightaverage molecular weight of about 150 to about 1,000,000 (morepreferably, about 1,000 to about 1,000,000).

A preferred class of useful polysiloxanes includes those that can berepresented by the following general formula:(OH)_(p)—Si(R′)_(3-p)-[G-Si(R′)₂]_(t)—O—[(R′)₂SiO]_(q)[Si(R′)₂-G]_(t)-Si(R′)_(3-p)—(OH)_(p)  (I)wherein each p is independently an integer of 1, 2, or 3 (preferably,1); each G is independently a divalent linking group; each R′ isindependently selected from alkyl, alkenyl, fluoroalkyl, aryl,fluoroaryl, cycloalkyl, fluorocycloalkyl, heteroalkyl,heterofluoroalkyl, heteroaryl, heterofluoroaryl, heterocycloalkyl,heterofluorocycloalkyl, and combinations thereof; q is an integer of 0to about 15,000 (preferably, about 20 to about 15,000); and each t isindependently an integer of 0 or 1 (preferably, 0). Preferably, each R′is independently selected from alkyl (preferably, having 1 to about 8carbon atoms), fluoroalkyl (preferably, having 3 to about 8 carbonatoms; more preferably, R_(f)C₂H₄—, wherein R_(f) is a fluorinated orperfluorinated alkyl group having 1 to about 6 carbon atoms (preferably,1 to about 6 carbon atoms)), aryl, and combinations thereof. Morepreferably, each R′ is independently selected from methyl, C₄F₉C₂H₄—,C₆F₁₃C₂H₄—, CF₃C₂H₄—, C₆H₅C₂H₄—, phenyl, and combinations thereof (evenmore preferably, methyl, CF₃C₂H₄—, phenyl, C₄F₉C₂H₄—, and combinationsthereof; most preferably, methyl). Each divalent linking group, G, ispreferably independently selected from oxy, alkylene, arylene,heteroalkylene, heteroarylene, cycloalkylene, heterocycloalkylene, andcombinations thereof (more preferably, selected from oxy, alkylene,arylene, and combinations thereof). Heteroatoms (in G and/or R′) caninclude oxygen, sulfur, nitrogen, phosphorus, and combinations thereof(preferably, oxygen, sulfur, and combinations thereof; more preferably,oxygen). G can contain fluorine, provided that it is separated fromsilicon by at least two carbon atoms.

Preferred polysiloxanes include hydroxyl-endblocked polydimethylsiloxanehomopolymer, as well as hydroxyl-endblocked copolymers comprisingdimethylsiloxane units and up to about 40 or 50 mole percent of otherunits selected from dialkylsiloxane units, (alkyl)(methyl)siloxaneunits, and (alkyl)(phenyl)siloxane units wherein each alkyl group isindependently selected from alkyl groups having two to about 8 carbonatoms (for example, hexyl), di(fluoroalkyl)siloxane units,(fluoroalkyl)(methyl)siloxane units, and (fluoroalkyl)(phenyl)siloxaneunits wherein each fluoroalkyl group is independently selected fromfluoroalkyl groups having 3 to about 8 carbon atoms (for example,trifluoropropyl or nonafluorohexyl), diphenylsiloxane units, andcombinations thereof.

The polysiloxanes useful as component (a) can be used in the curablecomposition of the invention singly or in the form of mixtures ofdifferent polysiloxanes. Sometimes mixtures can be preferred. Apreferred composition for use as component (a) comprises a mixture of(1) at least one polydiorganosiloxane, fluorinated polydiorganosiloxane,or combination thereof (preferably, at least one polydiorganosiloxane)having a weight average molecular weight in the range of about 300,000to about 1,000,000 (more preferably, about 400,000 to about 900,000;most preferably, about 500,000 to about 700,000) and (2) at least onepolydiorganosiloxane, fluorinated polydiorganosiloxane, or combinationthereof (preferably, at least one polydiorganosiloxane) having a weightaverage molecular weight in the range of about 150 to about 150,000(more preferably, about 10,000 to about 120,000; most preferably, about10,000 to about 15,000). The relative amounts of component (1) andcomponent (2) and their molecular weights can be selected for releaseapplications according to the nature of the adhesive (or other material)to be utilized and the level of release desired.

For example, for mold release applications, the weight ratio of theformer polysiloxane to the latter polysiloxane can range from about 3:1to about 19:1 (preferably, about 4:1 to about 9:1; more preferably,about 6:1). For pressure sensitive adhesive (PSA) release applications,the weight ratio of the former polysiloxane to the latter polysiloxanecan range, for example, from about 2:1 to about 1:10 (preferably, about1:1 to about 1:6; more preferably, about 1:2 to about 1:4).

The polysiloxanes suitable for use as component (a) can be prepared byknown synthetic methods and many are commercially available. Forexample, the hydroxysilyl-functional components of Syl-Off™ 292 coatingcomposition (available from Dow Corning Corporation, Midland, Mich.) arepreferred polysiloxanes, and other useful polysiloxanes of varyingmolecular weight can be obtained from Gelest, Inc., Morrisville, Pa.(see, for example, the polysiloxanes described in Silicon Compounds:Silanes and Silicones, Second Edition, edited by B. Arkles and G.Larson, Gelest, Inc. (2008)).

Component (b)

Polysiloxanes suitable for use as crosslinker component (b) of thecurable composition of the invention include polydiorganosiloxanes,fluorinated polydiorganosiloxanes, and combinations thereof comprisingreactive silane functionality comprising at least two hydrosilylmoieties (that is, monovalent moieties comprising a hydrogen atom bondeddirectly to a silicon atom). The polysiloxanes can be small molecules,oligomers, polymers, or a combination thereof. Preferably, thepolysiloxanes are polymers. The polysiloxanes can be linear, branched,or cyclic. Useful polymers include those that have random, alternating,block, or graft structures, or a combination thereof.

The molecular weight and the reactive silane functionality of component(b) (including the number and nature of the hydrosilyl moieties) canvary widely, depending upon, for example, the molecular weight and thereactive silane functionality of component (a) and the propertiesdesired for the curable and/or cured composition. Preferably, component(b) has an average reactive silane functionality of at least three (soas to enable the formation of a crosslinked network when component (a)is hydroxyl-endblocked). The polysiloxanes preferably have a weightaverage molecular weight of about 100 to about 100,000.

A preferred class of polysiloxanes includes those that can berepresented by the following general formula:R′₂R″SiO(R′₂SiO)_(r)(HR′SiO)_(s)SiR″R′₂  (II)wherein R′ is as defined above for Formula (I); each R″ is independentlyhydrogen or R′; r is an integer of 0 to about 150 (preferably, 0 toabout 100; more preferably, 0 to about 20); and s is an integer of 2 toabout 150 (preferably, about 5 to about 100; more preferably, about 20to about 80). Most preferably, both R″ and R′ are methyl, r is 0, and/ors is about 40.

Preferred hydride-functional polysiloxanes include those comprisingpolydimethylsiloxane homopolymer, as well as those comprisingcopolymer(s) comprising dimethylsiloxane units and up to about 40 or 50mole percent of other units selected from dialkylsiloxane units,(alkyl)(methyl)siloxane units, and (alkyl)(phenyl)siloxane units whereineach alkyl group is independently selected from alkyl groups having twoto about 8 carbon atoms (for example, hexyl), di(fluoroalkyl)siloxaneunits, (fluoroalkyl)(methyl)siloxane units, and(fluoroalkyl)(phenyl)siloxane units wherein each fluoroalkyl group isindependently selected from fluoroalkyl groups having 3 to about 8carbon atoms (for example, trifluoropropyl or nonafluorohexyl),diphenylsiloxane units, and combinations thereof. Although homopolymeris often preferred, copolymers can be preferred for some applications.

The polysiloxanes useful as component (b) can be used in the curablecomposition of the invention singly or in the form of mixtures ofdifferent polysiloxanes. The polysiloxanes can be prepared by knownsynthetic methods and many are commercially available. For example,Syl-Off™ Q2-7560 crosslinker, Syl-Off™ 7678 crosslinker, and thehydrosilyl-functional component (for example, Syl-Off™ 7048 crosslinker)of Syl-Off™ 292 and Syl-Off™ 294 coating compositions (all availablefrom Dow Corning Corporation, Midland, Mich.) are preferredpolysiloxanes, and other useful polysiloxane crosslinkers of varyingmolecular weight can be obtained from Gelest, Inc., Morrisville, Pa.(see, for example, the polysiloxanes described in Silicon Compounds:Silanes and Silicones, Second Edition, edited by B. Arkles and G.Larson, Gelest, Inc. (2008)).

Component (c)

Photoactivatable compositions suitable for use as component (c) of thecurable composition of the invention include compositions (known orhereafter-developed compounds or mixtures) that, upon exposure toradiation (preferably, ultraviolet radiation, visible radiation, or acombination thereof), generate at least one base selected from amidines,guanidines (including substituted guanidines such as biguanides),phosphazenes, proazaphosphatranes (also known as Verkade's bases), andcombinations thereof. Photoactivatable compositions that generateself-protonatable forms of the bases (for example, aminoacids such asarginine) generally are less suitable and therefore excluded, as suchforms of the bases are self-neutralized. Preferred photoactivatablecompositions include those that, upon exposure to radiation, generate atleast one base selected from amidines, guanidines, and combinationsthereof (more preferably, amidines and combinations thereof mostpreferably, cyclic amidines and combinations thereof).

It has been discovered that the bases of the listed structural classescan effectively catalyze reaction between components (a) and (b), asdescribed above. The bases (and their photoactivatable precursors) canbe used in the curable composition singly (individually) or in the formof mixtures (including different structural classes).

Useful photoactivatable compositions include those that, upon exposureto radiation, generate amidines that can be represented by the followinggeneral formula:

wherein R1, R2, R3, and R4 are each independently selected fromhydrogen, monovalent organic groups, monovalent heteroorganic groups(for example, comprising nitrogen, oxygen, phosphorus, or sulfur in theform of groups or moieties that are bonded through a carbon atom andthat do not contain acid functionality such as carboxylic or sulfonic),and combinations thereof; and wherein any two or more of R1, R2, R3, andR4 optionally can be bonded together to form a ring structure(preferably, a five-, six-, or seven-membered ring; more preferably, asix- or seven-membered ring). The organic and heteroorganic groupspreferably have from 1 to about 20 carbon atoms (more preferably, from 1to about 10 carbon atoms; most preferably, from 1 to about 6 carbonatoms). Preferably, R4 is not hydrogen.

Photoactivatable compositions that can generate amidines comprising atleast one ring structure (that is, cyclic amidines) are generallypreferred. Photoactivatable compositions that can generate cyclicamidines comprising two ring structures (that is, bicyclic amidines) aremore preferred.

Representative examples of useful photoactivatable compositions includethose that can generate amidine compounds such as1,2-dimethyl-1,4,5,6-tetrahydropyrimidine,1-ethyl-2-methyl-1,4,5,6-tetrahydropyrimidine,1,2-diethyl-1,4,5,6-tetrahydropyrimidine,1-n-propyl-2-methyl-1,4,5,6-tetrahydropyrimidine,1-isopropyl-2-methyl-1,4,5,6-tetrahydropyrimidine,1-ethyl-2-n-propyl-1,4,5,6-tetrahydropyrimidine,1-ethyl-2-isopropyl-1,4,5,6-tetrahydropyrimidine, DBU (that is,1,8-diazabicyclo[5.4.0]-7-undecene), DBN (that is,1,5-diazabicyclo[4.3.0]-5-nonene), and the like, and combinationsthereof. Preferred photoactivatable compositions include those that cangenerate amidines such as 1,2-dimethyl-1,4,5,6-tetrahydropyrimidine, DBU(that is, 1,8-diazabicyclo[5.4.0]-7-undecene), DBN (that is,1,5-diazabicyclo[4.3.0]-5-nonene), and combinations thereof, with thosethat can generate DBU, DBN, and combinations thereof being morepreferred and those that can generate DBU most preferred.

Useful photoactivatable compositions include those that, upon exposureto radiation, generate guanidines that can be represented by thefollowing general formula:

wherein R1, R2, R3, R4, and R5 are each independently selected fromhydrogen, monovalent organic groups, monovalent heteroorganic groups(for example, comprising nitrogen, oxygen, phosphorus, or sulfur in theform of groups or moieties that are bonded through a carbon atom andthat do not contain acid functionality such as carboxylic or sulfonic),and combinations thereof; and wherein any two or more of R1, R2, R3, R4,and R5 optionally can be bonded together to form a ring structure(preferably, a five-, six-, or seven-membered ring; more preferably, afive- or six-membered ring; most preferably, a six-membered ring). Theorganic and heteroorganic groups preferably have from 1 to about 20carbon atoms (more preferably, from 1 to about 10 carbon atoms; mostpreferably, from 1 to about 6 carbon atoms). Preferably, R5 is nothydrogen.

Photoactivatable compositions that can generate guanidines comprising atleast one ring structure (that is, cyclic guanidines) are generallypreferred. Photoactivatable compositions that can generate cyclicguanidines comprising two ring structures (that is, bicyclic guanidines)are more preferred.

Representative examples of useful photoactivatable compositions includethose that can generate guanidine compounds such as 1-methylguanidine,1-n-butylguanidine, 1,1-dimethylguanidine, 1,1-diethylguanidine,1,1,2-trimethylguanidine, 1,2,3-trimethylguanidine,1,3-diphenylguanidine, 1,1,2,3,3-pentamethylguanidine,2-ethyl-1,1,3,3-tetramethylguanidine,1,1,3,3-tetramethyl-2-n-propylguanidine,1,1,3,3-tetramethyl-2-isopropylguanidine,2-n-butyl-1,1,3,3-tetramethylguanidine,2-tert-butyl-1,1,3,3-tetramethylguanidine, 1,2,3-tricyclohexylguanidine,TBD (that is, 1,5,7-triazabicyclo[4.4.0]dec-5-ene), MTBD (that is,7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene),7-ethyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene,7-n-propyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene,7-isopropyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene,7-n-butyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene,7-isobutyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene,7-tert-butyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene,7-cyclohexyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene,7-n-octyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene,7-2-ethylhexyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene,7-decyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene, biguanide,1-methylbiguanide, 1-n-butylbiguanide, 1-(2-ethylhexyl)biguanide,1-n-octadecylbiguanide, 1,1-dimethylbiguanide, 1,1-diethylbiguanide,1-cyclohexylbiguanide, 1-allylbiguanide, 1-n-butyl-N2-ethylbiguanide,1,1′-ethylenebisguanide, 1-[3-(diethylamino)propyl]biguanide,1-[3-(dibutylamino)propyl]biguanide,N′,N″-dihexyl-3,12-diimino-2,4,11,13-tetraazatetradecanediamidine, andthe like, and combinations thereof. Preferred photoactivatablecompositions include those that can generate guanidines such as TBD(that is, 1,5,7-triazabicyclo[4.4.0]dec-5-ene), MTBD (that is,7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene),2-tert-butyl-1,1,3,3-tetramethylguanidine, and combinations thereof.More preferred photoactivatable compositions include those that cangenerate TBD, MTBD, and combinations thereof.

If desired, photoactivatable compositions that can generate amidinesand/or guanidines exhibiting a pH value lower than 13.4 when measuredaccording to JIS Z 8802 (for example, 1,3-diphenylguanidine, DBU, DBN,or a combination thereof; preferably, DBU, DBN, or a combinationthereof) can be utilized. The referenced method for determining the pHof aqueous solutions, JIS Z 8802, is carried out by first preparing anaqueous solution of base by adding 5 millimoles of base to 100 g of amixed solvent composed of isopropyl alcohol and water in a weight ratioof 10:3. The pH of the resulting solution is then measured at 23° C.using a pH meter (for example, a Horiba Seisakusho Model F-22 pH meter).

Useful photoactivatable compositions further include those that, uponexposure to radiation, generate phosphazenes that can be represented bythe following general formula:

wherein R1, R2, R3, R4, R5, R6, and R7 are each independently selectedfrom hydrogen, monovalent organic groups, monovalent heteroorganicgroups (for example, comprising nitrogen, oxygen, phosphorus, or sulfurin the form of groups or moieties that are bonded through a carbon atomand that do not contain acid functionality such as carboxylic orsulfonic), and combinations thereof; and wherein any two or more of R1,R2, R3, R4, R5, R6, and R7 optionally can be bonded together to form aring structure (preferably, a five-, six-, or seven-membered ring; morepreferably, a five- or six-membered ring; most preferably, asix-membered ring). The organic and heteroorganic groups preferably havefrom 1 to about 20 carbon atoms (more preferably, from 1 to about 10carbon atoms; most preferably, from 1 to about 6 carbon atoms).Preferably, R7 is not hydrogen.

Representative examples of useful photoactivatable compositions includethose that can generate phosphazene compounds such as

and the like, and combinations thereof. Preferred photoactivatablecompositions include those that can generate phosphazenes such as2-tert-butylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2-diazaphosphorine,phosphazene base P₁-t-Bu-tris(tetramethylene), phosphazene base P₄-t-Bu,and combinations thereof.

Useful photoactivatable compositions also further include those that,upon exposure to radiation, generate proazaphosphatrane bases (Verkade'sbases) that can be represented by the following general formula:

wherein R1, R2, and R3 are each independently selected from hydrogen,monovalent organic groups, monovalent heteroorganic groups (for example,comprising nitrogen, oxygen, phosphorus, or sulfur in the form of groupsor moieties that are bonded through a carbon atom and that do notcontain acid functionality such as carboxylic or sulfonic), andcombinations thereof (less preferably hydrogen). The organic andheteroorganic groups preferably have from 1 to about 20 carbon atoms(more preferably, from 1 to about 10 carbon atoms; most preferably, from1 to about 6 carbon atoms).

Representative examples of useful photoactivatable compositions includethose that can generate proazaphosphatrane compounds such as

and the like, and combinations thereof. Preferred photoactivatablecompositions include those that can generate2,8,9-triisopropyl-2,5,8,9-tetraaza-1-phosphabicyclo[3.3.3]undecane.

Suitable photoactivatable compositions for use in generating theabove-described bases are known. For example, salts that can generateamidine or guanidine bases upon thermal activation (for example, atelevated temperatures or upon exposure to infrared radiation) aredescribed in U.S. Pat. No. 5,219,958 (Noomen et al.), the descriptionsof which salts are incorporated herein by reference. A quaternaryammonium salt (namely,8-(4′-benzoylphenylmethyl)-8-azania-1-aza-bicyclo[5.4.0]undec-7-enebenzo[o]mate) that generates DBU upon irradiation has been described byK. Suyama et al., Journal of Photopolymer Science and Technology 19(1),81 (2006), the description of this salt and its synthesis beingincorporated herein by reference. U.S. Pat. No. 6,124,371 (Stanssens etal.) describes photolabile compounds of the structural formula Z-A(wherein Z is a photolabile group, A is a strong base, and Z iscovalently bound to A) that can liberate amidine or guanidine bases uponirradiation (for example, ultraviolet light, electron beam, infrared, orlaser irradiation), the descriptions of which compounds are alsoincorporated herein by reference.

U.S. Pat. No. 6,277,986 (Hall-Goule et al.) describes α-amino ketones(comprising an aromatic or heteroaromatic radical that is capable ofabsorbing light in the wavelength range of 200 to 650 nanometers (nm))from which amidine bases can be liberated upon irradiation (with visibleor ultraviolet light), the descriptions of which ketones areincorporated herein by reference. U.S. Pat. No. 6,551,761 (Hall-Goule etal.) describes photoactivatable nitrogen-containing salts includingtetraaryl- and triarylalkylborate salts of, for example, α-amidiniumketones. The photoactivatable salts can release amidine, guanidine, orphosphazene (and apparently, by extension, proazaphosphatrane) basesupon exposure to visible or ultraviolet light, the descriptions of thephotoactivatable salts being incorporated herein by reference.

Preferred photoactivatable compositions for use in the curablecomposition of the invention include those described in U.S. Pat. No.7,538,104 (Baudin et al.), the descriptions of which compositions (andmethods for their preparation) are incorporated herein by reference. Thecompositions comprise at least one 1,3-diamine compound that issubstituted on at least one nitrogen atom by at least one aralkylradical. The aralkyl radical preferably comprises at least one aromaticor heteroaromatic radical that absorbs light in the wavelength range of200 nm to 650 nm. Absorption of the light results in a photoeliminationthat leads to the generation of an amidine or guanidine.

A preferred class of such photoactivatable compositions comprises atleast one 1,3-diamine compound selected from those that are representedby the formulaN(R₇)(R₆)—CH(R₅)—N(R₄)—C(R₁)(R₂)(R₃)  (VII)wherein R₁ is selected from aromatic radicals, heteroaromatic radicals,and combinations thereof that absorb light in the wavelength range from200 nm to 650 nm and that are unsubstituted or substituted one or moretimes by at least one monovalent group selected from C₁-C₁₈ alkyl,C₂-C₁₈ alkenyl, C₂-C₁₈ alkynyl, C₁-C₁₈ haloalkyl, —NO₂, —NR₁₀R₁₁, —CN,—OR₁₂, —SR₁₂, —C(O)R₁₃, —C(O)OR₁₄, halogen, groups of the formulaN(R₇)(R₆)—CH(R₅)—N(R₄)—C(R₂)(R₃)— where R₂-R₇ are as defined for FormulaVII, and combinations thereof, and that upon said absorption bring abouta photoelimination that generates an amidine or guanidine; R₂ and R₃ areeach independently selected from hydrogen, C₁-C₁₈ alkyl, phenyl,substituted phenyl (that is, substituted one or more times by at leastone monovalent group selected from C₁-C₁₈ alkyl, —CN, —OR₁₂, —SR₁₂,halogen, C₁-C₁₈ haloalkyl, and combinations thereof), and combinationsthereof; R₅ is selected from C₁-C₁₈ alkyl, —NR₈, R₉, and combinationsthereof; R₄, R₆, R₇, R₈, R₉, R₁₀ and R₁₁ are each independently selectedfrom hydrogen, C₁-C₁₈ alkyl, and combinations thereof; or R₄ and R₆together form a C₂-C₁₂ alkylene bridge that is unsubstituted or issubstituted by one or more monovalent groups selected from C₁-C₄ alkylradicals and combinations thereof; or R₅ and R₇, independently of R₄ andR₆, together form a C₂-C₁₂ alkylene bridge that is unsubstituted or issubstituted by one or more monovalent groups selected from C₁-C₄ alkylradicals and combinations thereof; or, if R₅ is —NR₈R₉, then R₇ and R₉together form a C₂-C₁₂ alkylene bridge that is unsubstituted or issubstituted by one or more monovalent groups selected from C₁-C₄ alkylradicals and combinations thereof; R₁₂ and R₁₃ are each independentlyselected from hydrogen, C₁-C₁₉ alkyl, and combinations thereof; and R₁₄is selected from C₁-C₁₉ alkyl and combinations thereof.

The alkyl and haloalkyl groups can be linear or branched and,preferably, contain 1 to about 12 carbon atoms (more preferably, 1 toabout 6 carbon atoms). Halogen atoms preferably are chlorine, fluorine,and/or bromine (more preferably, chlorine and/or fluorine). The alkenylgroups can be linear or branched and, preferably, contain 2 to about 12carbon atoms (more preferably, 2 to about 6 carbon atoms). The alkynylgroups can be linear or branched and, preferably, contain 2 to about 12carbon atoms (more preferably, 2 to about 6 carbon atoms).

Preferred 1,3-diamine compounds of Formula VII include those wherein R₁is selected from substituted and unsubstituted phenyl, naphthyl,phenanthryl, anthryl, pyrenyl, 5,6,7,8-tetrahydro-2-naphthyl,5,6,7,8-tetrahydro-1-naphthyl, thienyl, benzo[b]thienyl,naphtho[2,3-b]thienyl, thianthrenyl, anthraquinonyl, dibenzofuryl,chromenyl, xanthenyl, thioxanthyl, phenoxathiinyl, pyrrolyl, imidazolyl,pyrazolyl, pyrazinyl, pyrimidinyl, pyridazinyl, indolizinyl, isoindolyl,indolyl, indazolyl, purinyl, quinolizinyl, isoquinolyl, quinolyl,phthalazinyl, naphthyridinyl, quinoxalinyl, quinazolinyl, cinnolinyl,pteridinyl, carbazolyl, β-carbolinyl, phenanthridinyl, acridinyl,perimidinyl, phenanthrolinyl, phenazinyl, isothiazolyl, phenothiazinyl,isoxazolyl, furazanyl, terphenyl, stilbenzyl, fluorenyl, phenoxazinyl,and combinations thereof, these radicals being unsubstituted orsubstituted one or more times by C₁-C₁₈ alkyl, C₂-C₁₈ alkenyl, C₂-C₁₈alkynyl, C₁-C₁₈ haloalkyl, —NO₂, —NR₁₀R₁₁, —CN, —OR₁₂, —SR₁₂, —C(O)R₁₃,—C(O)OR₁₄, halogen, a radical of the formulaN(R₇)(R₆)—CH(R₅)—N(R₄)—C(R₂)(R₃)—, or a combination thereof, where R₂-R₇and R₁₀-R₁₄ are as defined for Formula VII, or R₁ is a substituted orunsubstituted biphenylyl radical, wherein each phenyl group isindependently substituted with from zero to three (preferably, zero orone) substituents selected from C₁-C₁₈ alkyl, C₂-C₁₈ alkenyl, —OH, —CN,—OR₁₀, —SR₁₀, halogen, radicals of the formulaN(R₇)(R₆)—CH(R₅)—N(R₄)—C(R₂)(R₃)—, and combinations thereof, where R₂-R₇and R₁₀-R₁₄ are as defined for Formula VII.

More preferably, R₁ is selected from substituted and unsubstitutedphenyl, naphthyl, anthryl, anthraquinon-2-yl, biphenylyl, pyrenyl,thioxanthyl, thianthrenyl, phenothiazinyl, and combinations thereof(even more preferably, R₁ is selected from substituted and unsubstitutedphenyl, anthryl, naphthyl, anthraquinon-2-yl, biphenylyl, andcombinations thereof; still more preferably, R₁ is selected from phenyl,4-methylphenyl, biphenylyl, 2,4,6-trimethylphenyl, 4-cyanophenyl,3-cyanophenyl, 2-chlorophenyl, 2,6-dichlorophenyl, 3-methoxyphenyl,4-methoxyphenyl, 4-ethenylphenyl, 4-methylthiophenyl,4-trifluoromethylphenyl, 2-nitrophenyl, 2,4,6-trimethoxyphenyl,2,4-dimethoxyphenyl, naphthyl, anthryl, anthraquinon-2-yl, andcombinations thereof, or is selected from the aforementioned radicalssubstituted with a radical of the formulaN(R₇)(R₆)—CH(R₅)—N(R₄)—C(R₂)(R₃)—, where R₂-R₇ are as defined forFormula VII; most preferably, R₁ is selected from phenyl,3-methoxyphenyl, 4-methoxyphenyl, 2,4,6-trimethoxyphenyl,2,4-dimethoxyphenyl, and combinations thereof).

Preferably, R₂ and R₃ each are independently selected from hydrogen,C₁-C₆ alkyl, and combinations thereof (more preferably, both arehydrogen); R₄ and R₆ together form a C₂-C₆ alkylene (preferably, C₃alkylene) bridge that is unsubstituted or is substituted by one or moregroups selected from C₁-C₄ alkyl radicals and combinations thereof;and/or R₅ and R₇ together form a C₂-C₆ alkylene (preferably, C₃ or C₅alkylene) bridge that is unsubstituted or is substituted by one or moregroups selected from C₁-C₄ alkyl radicals and combinations thereof, or,if R₅ is —NR₈, R₉ (which is less preferable, as guanidine bases aresomewhat less preferred than amidine bases), R₉ and R₇ together form aC₂-C₆ alkylene bridge that is unsubstituted or substituted by one ormore groups selected from C₁-C₄ alkyl radicals and combinations thereof.

Representative examples of useful photoactivatable compositions includethose that comprise at least one compound selected from5-benzyl-1,5-diazabicyclo[4.3.0]nonane,5-(anthracen-9-yl-methyl)-1,5-diaza[4.3.0]nonane,5-(2′-nitrobenzyl)-1,5-diazabicyclo[4.3.0]nonane,5-(4′-cyanobenzyl)-1,5-diazabicyclo[4.3.0]nonane,5-(3′-cyanobenzyl)-1,5-diazabicyclo[4.3.0]nonane,5-(anthraquinon-2-yl-methyl)-1,5-diaza[4.3.0]nonane,5-(2′-chlorobenzyl)-1,5-diazabicyclo[4.3.0]nonane,5-(4′-methylbenzyl)-1,5-diazabicyclo[4.3.0]nonane,5-(2′,4′,6′-trimethylbenzyl)-1,5-diazabicyclo[4.3.0]nonane,5-(4′-ethenylbenzyl)-1,5-diazabicyclo[4.3.0]nonane,5-(3′-trimethylbenzyl)-1,5-diazabicyclo[4.3.0]nonane,5-(2′,3′-dichlorobenzyl)-1,5-diazabicyclo[4.3.0]nonane,5-(naphth-2-yl-methyl-1,5-diazabicyclo[4.3.0]nonane,1,4-bis(1,5-diazabicyclo[4.3.0]nonanylmethyl)benzene,8-benzyl-1,8-diazabicyclo[5.4.0]undecane,8-benzyl-6-methyl-1,8-diazabicyclo[5.4.0]undecane,9-benzyl-1,9-diazabicyclo[6.4.0]dodecane,10-benzyl-8-methyl-1,10-diazabicyclo[7.4.0]tridecane,11-benzyl-1,1′-diazabicyclo[8.4.0]tetradecane,8-(2′-chlorobenzyl)-1,8-diazabicyclo[5.4.0]undecane,8-(2′,6′-dichlorobenzyl)-1,8-diazabicyclo[5.4.0]undecane,4-(diazabicyclo[4.3.0]nonanylmethyl)-1,1′-biphenyl,4,4′-bis(diazabicyclo[4.3.0]nonanylmethyl)-11′-biphenyl,5-benzyl-2-methyl-1,5-diazabicyclo[4.3.0]nonane,5-benzyl-7-methyl-1,5,7-triazabicyclo[4.4.0]decane, and the like, andcombinations thereof.

A preferred group of photoactivatable compositions includes those thatcomprise at least one compound selected from5-benzyl-1,5-diazabicyclo[4.3.0]nonane,5-(anthracen-9-yl-methyl)-1,5-diaza[4.3.0]nonane,5-(2′-nitrobenzyl)-1,5-diazabicyclo[4.3.0]nonane,5-(4′-cyanobenzyl)-1,5-diazabicyclo[4.3.0]nonane,5-(3′-cyanobenzyl)-1,5-diazabicyclo[4.3.0]nonane,5-(anthraquinon-2-yl-methyl)-1,5-diaza[4.3.0]nonane,5-(2′-chlorobenzyl)-1,5-diazabicyclo[4.3.0]nonane,5-(4′-methylbenzyl)-1,5-diazabicyclo[4.3.0]nonane,5-(2′,4′,6′-trimethylbenzyl)-1,5-diazabicyclo[4.3.0]nonane,5-(4′-ethenylbenzyl)-1,5-diazabicyclo[4.3.0]nonane,5-(3′-trimethylbenzyl)-1,5-diazabicyclo[4.3.0]nonane,5-(2′,3′-dichlorobenzyl)-1,5-diazabicyclo[4.3.0]nonane,5-(naphth-2-yl-methyl-1,5-diazabicyclo[4.3.0]nonane,1,4-bis(1,5-diazabicyclo[4.3.0]nonanylmethyl)benzene,8-benzyl-1,8-diazabicyclo[5.4.0]undecane,8-benzyl-6-methyl-1,8-diazabicyclo[5.4.0]undecane,8-(2′-chlorobenzyl)-1,8-diazabicyclo[5.4.0]undecane,8-(2′,6′-dichlorobenzyl)-1,8-diazabicyclo[5.4.0]undecane,4-(diazabicyclo[4.3.0]nonanylmethyl)-1,1′-biphenyl,4,4′-bis(diazabicyclo[4.3.0]nonanylmethyl)-11′-biphenyl,5-benzyl-2-methyl-1,5-diazabicyclo[4.3.0]nonane,5-benzyl-7-methyl-1,5,7-triazabicyclo[4.4.0]decane, and combinationsthereof.

A second preferred group of photoactivable compositions includes thosethat comprise at least one compound selected from8-benzyl-1,8-diazabicyclo[5.4.0]undecane,8-benzyl-6-methyl-1,8-diazabicyclo[5.4.0]undecane,9-benzyl-1,9-diazabicyclo[6.4.0]dodecane,10-benzyl-8-methyl-1,10-diazabicyclo[7.4.0]tridecane,11-benzyl-1,1′-diazabicyclo[8.4.0]tetradecane, and combinations thereof.Most preferred are photoactivatable compositions that comprise at leastone compound selected from 8-benzyl-1,8-diazabicyclo[5.4.0]undecane,8-benzyl-6-methyl-1,8-diazabicyclo[5.4.0]undecane, and combinationsthereof.

The photoactivatable compositions can optionally (but preferably)further comprise at least one photosensitizer (for example, a compoundhaving an absorption spectrum that overlaps or closely matches theemission spectrum of the radiation source to be used and that canimprove the overall quantum yield by means of, for example, energytransfer or electron transfer to other component(s) of thephotoactivatable composition). Useful photosensitizers include aromaticketones (for example, substituted or unsubstituted benzophenones,substituted or unsubstituted thioxanthones, substituted or unsubstitutedanthraquinones, and the like, and combinations thereof), dyes (forexample, oxazines, acridines, phenazines, rhodamines, and the like, andcombinations thereof), and the like, and combinations thereof. Preferredphotosensitizers include aromatic ketones and combinations thereof (morepreferably, substituted or unsubstituted benzophenones, substituted orunsubstituted thioxanthones, and combinations thereof; most preferably,substituted or unsubstituted benzophenones and combinations thereof).The amount of photosensitizer can vary widely, depending upon, forexample, its nature, the nature of other component(s) of thephotoactivatable composition, and the particular curing conditions. Forexample, amounts ranging from about 0.1 weight percent to about 0.5weight percent can be useful for some applications.

Preparation of Curable Composition

The curable composition of the invention can be prepared by combiningcomponents (a), (b), and (c) in essentially any order (preferably, withagitation or stirring). Preferably, components (a) and (b) are combinedinitially, followed by addition of component (c). The composition can bemaintained as a relatively shelf-stable, 1-part system (comprising allthree components) in the substantial absence of radiation of anactivating wavelength. The composition can be stable under suchconditions for periods of up to, for example, days or weeks (arelatively long pot life), prior to coating or other application of thecomposition, with or without the addition of solvent (which isoptional).

The relative amounts of components (a) and (b) can vary widely,depending upon their nature and the desired properties of the curableand/or cured composition. Although stoichiometry prescribes a 1:1 molarratio of reactive silane functionality (for example, one mole ofhydrosilyl moieties for every mole of hydroxysilyl moieties), inpractice it can be useful to have a deficiency or an excess ofhydrosilyl functionality (for example, this can be useful when cureinhibitors are present). Molar ratios (of hydrosilyl moieties tohydroxysilyl moieties) up to, for example, about 8:1 or about 13:1 oreven as high as about 35:1 can be useful. Component (c) (thephotoactivatable composition(s)) can be present in the curablecomposition in amounts ranging, for example, from about 0.1 to about 10weight percent (preferably, from about 0.1 to about 5 weight percent;more preferably, from about 0.5 to about 2 weight percent), based uponthe total weight of components (a), (b), and (c).

If desired, the curable composition can comprise at least one solvent ordiluent to aid in storage stability, mixing, and/or coating,particularly when components (a) and (b) are polymeric. Suitablesolvents for use in the curable composition of the invention includeaprotic solvents such as aromatic solvents (for example, xylene,toluene, 1,2-dichlorobenzene, 1,3-dichlorobenzene, 1,4-dichlorobenzene,and the like, and mixtures thereof), ketones (for example, methyl ethylketone (MEK), cyclohexanone, and the like, and mixtures thereof), alkylesters (for example, ethyl acetate, butyl acetate, and the like, andmixtures thereof), alkanes (for example, heptane, isoparaffinichydrocarbons, and the like, and mixtures thereof), ethers (for example,t-butyl methyl ether, tetrahydrofuran (THF), and the like, and mixturesthereof), and the like, and mixtures thereof. Preferred solvents includearomatic solvents, alkanes, ketones, and mixtures thereof with xylene,heptane, methyl ethyl ketone, and mixtures thereof being more preferredand heptane, methyl ethyl ketone, and mixtures thereof most preferred.

Minor amounts of optional components can be added to the curablecomposition to impart particular desired properties for particularcuring methods or uses. Useful compositions can comprise conventionaladditives such as, for example, catalysts (including conventionalcondensation catalysts such as tin catalysts, which can be added asco-catalysts if desired), initiators, surfactants, stabilizers, thermalinhibitors, anti-oxidants, flame retardants, adhesion promoters, releasemodifiers (for example, silicate MQ resin), colorants, and the like, andmixtures thereof.

Use and Curing of Curable Composition

The curable composition of the invention can be used in variousdifferent applications. For example, the composition(s) can be used assealants, release coatings, surface treatments, hardcoats, and the like.When used as fluorinated surface treatments, a degree of hydrophobicityand/or oleophobicity can be imparted to a variety of substrates (forexample, for surface protection or to enhance ease of cleaning).

The curable composition of the invention (or, alternatively, itscomponents) can be applied to at least a portion of at least one majorsurface of a substrate (for example, a sheet, a fiber, or a shapedobject) by essentially any known or hereafter-developed applicationmethod, so as to form a variety of different coated articles. Thecomposition can be applied in essentially any manner (and withessentially any thickness) that can form a useful coating.

Useful application methods include coating methods such as dip coating,spin coating, spray coating, wiping, roll coating, and the like, andcombinations thereof. The composition can be applied in neat form or inthe form of solvent solutions (for example, in solvents such as alkylesters, ketones, alkanes, aromatics, and the like, and mixturesthereof). When solvent is used, useful concentrations of the compositioncan vary over a wide range (for example, from about 1 to about 90 weightpercent), depending upon the viscosity of the composition, theapplication method utilized, the nature of the substrate, and thedesired properties.

Substrates suitable for use in preparing the coated articles includethose having at least one surface comprising a material that is solidand preferably substantially inert to any coating or application solventthat is used. Preferably, the curable composition can adhere to thesubstrate surface through chemical interactions, physical interactions,or a combination thereof (more preferably, a combination thereof).

Suitable substrates can comprise a single material or a combination ofdifferent materials and can be homogeneous or heterogeneous in nature.Useful heterogeneous substrates include coated substrates comprising acoating of a material (for example, a metal or a primer) borne on aphysical support (for example, a polymeric film).

Useful substrates include those that comprise wood, glass, minerals (forexample, both man-made ceramics such as concrete and naturally-occurringstones such as marble and the like), polymers (for example,polycarbonate, polyester, polyacrylate, and the like), metals (forexample, copper, silver, gold, aluminum, iron, stainless steel, nickel,zinc, and the like), metal alloys, metal compounds (for example, metaloxides and the like), leather, parchment, paper, textiles, paintedsurfaces, and combinations thereof. Preferred substrates include glass,minerals, wood, metals, metal alloys, metal compounds, polymers, andcombinations thereof (more preferably, metals, metal alloys, metalcompounds, polymers, and combinations thereof).

Preferred substrates include those used for pressure-sensitive adhesive(PSA) products. For example, the curable composition can be applied tosuitable flexible or inflexible backing materials and then cured. Usefulflexible backing materials include paper, Kraft paper, polyolefin-coatedpaper, plastic films (for example, poly(propylene), poly(ethylene),poly(vinyl chloride), polyester (including poly(ethylene terephthalate),polyamide, cellulose acetate, and ethyl cellulose), and the like, andcombinations thereof, although essentially any surface requiring releasetoward adhesives can be utilized. Backings can thus also be of wovenfabric formed of threads of synthetic or natural materials such ascotton, nylon, rayon, glass, or ceramic material, or they can be ofnonwoven fabric such as air-laid webs of natural or synthetic fibers orblends of these. In addition, suitable backings can be formed of metal,metallized polymeric film, or ceramic sheet material. Primers can beutilized, but they are not always necessary.

The curable composition of the invention can provide coatings that aresuitable for use in the manufacture of PSA-coated labels and tapes. Thespecific level of release provided upon curing can be controllablyvaried through variation in, for example, the weight percentage andmolecular weight of component (a) of the composition, or through theaddition of release modifiers (for example, silicate MQ resin), whichalso can be varied in nature and/or amount.

The curable composition can be cured by exposing at least a portion ofthe composition to radiation of an appropriate wavelength to activatethe photoactivatable composition. The preferred curing conditions willvary, depending upon the particular application and its accompanyingrequirements and conditions. Moisture can be present but generally isnot necessary.

The preferred radiation source and exposure time will vary dependingupon, for example, the nature and amount of the photoactivatablecomposition. Sources of ultraviolet, visible, and/or infrared radiationcan be useful (for example, wavelengths ranging from about 200 nm toabout 650 or 700 nm or up to about 20,000 nm; preferably, ultravioletradiation, visible radiation, or a combination thereof). Suitableradiation includes sunlight and light from artificial sources, includingboth point sources and flat radiators.

Representative examples of useful radiation sources include carbon arclamps; xenon arc lamps; medium-pressure, high-pressure, and low-pressuremercury lamps, doped if desired with metal halides (metal halogenlamps); microwave-stimulated metal vapor lamps; excimer lamps;superactinic fluorescent tubes; fluorescent lamps; incandescent argonlamps; electronic flashlights; xenon flashlights; photographic floodlamps; electron beams; X-rays, produced by means of synchrotrons orlaser plasma; laser light sources (for example, excimer lasers); and thelike; and combinations thereof. The distance between the radiationsource and the coated substrate can vary widely, depending upon theparticular application and the type and/or power of the radiation source(for example, distances ranging from about 2 cm to about 150 cm can beuseful).

Cure generally can be effected by carrying out irradiation and/orsubsequent processing of the coated substrate at temperatures rangingfrom room temperature (for example, about 20-23° C.) up to about 150° C.or more (preferably, temperatures of about 20° C. to about 125° C.; morepreferably, about 20° C. to about 100° C.; most preferably, about 20° C.to about 80° C.). Curing times can range from a few seconds or less (forexample, at room temperature with adequate amounts of catalyst and lightexposure) to minutes or hours (for example, under low catalyst and/orlow light conditions).

Release coatings obtained via cure of the curable composition of theinvention generally contain little or no free silicone to adverselyaffect the tack and peel properties of PSAs that come in contact withthem. The curable composition of the invention can cure relativelyrapidly to provide relatively firmly anchored, highly crosslinked,solvent-resistant, tack-free coatings, which can be used with a broadrange of PSA types (for example, acrylates, tackified natural rubbers,and tackified synthetic elastomers).

Articles in the form of PSA laminates (for example, comprising a layerof PSA borne on a release liner) can be prepared by placing a PSA layerin contact with the release coating through dry lamination, wet solutioncasting, or even by application of a photopolymerizable composition tothe release coating, followed by irradiation to effectphotopolymerization (for example, as described in U.S. Pat. No.4,181,752 (Martens et al.), the description of which is incorporatedherein by reference). Such articles can exhibit relatively good storagestability (as evidenced, for example, by the results of room temperatureand/or heat accelerated aging tests to evaluate any change in the levelof release (peel force) from the release coating and/or in thesubsequent level of adhesion to a desired substrate).

EXAMPLES

Objects and advantages of this invention are further illustrated by thefollowing examples, but the particular materials and amounts thereofrecited in these examples, as well as other conditions and details,should not be construed to unduly limit this invention. These examplesare merely for illustrative purposes only and are not meant to belimiting on the scope of the appended claims.

Materials

Unless otherwise noted, all parts, percentages, ratios, etc., in theexamples and in the remainder of the specification are by weight. Unlessotherwise noted, all chemicals were obtained from, or are availablefrom, chemical suppliers such as Aldrich Chemical Company, Milwaukee,Wis.

Preliminary Screening of Bases 1-10 and Comparative Bases C-1-C-12

A sample of a 30 weight percent solids dispersion of a blend of reactivehydroxysilyl-functional siloxane polymer(s) (said to comprisehydroxyl-terminated polydimethylsiloxane) and hydrosilyl-functionalpolysiloxane crosslinker (said to comprisepoly(methyl)(hydrogen)siloxane) in xylene (a premium release coatingcomposition obtained from Dow Corning Corporation, Midland, Mich., underthe trade designation Syl-Off™ 292) was diluted to 10 weight percentsolids with heptane. For each of Bases 1-10 and Comparative BasesC-1-C-12, 0.02 g of base (listed in Table 1 below; all bases wereobtained from Aldrich Chemical Company, Milwaukee, Wis.) was added to 5g of Syl-Off™ 292 solution (10 weight percent in heptane) and thenmixed. The resulting mixtures were coated on the primed side of a 50micrometer thick polyester terephthalate (PET) film (obtained fromMitsubishi Polyester Film, Greer, SC, under the trade designationHostaphan™ 3SAB, referred to hereinafter as 3SAB PET film, which has oneside chemically treated or primed to improve the adhesion of siliconecoatings) using a number 4 rod. The resulting coated 3SAB PET sampleswere set aside at room temperature (about 23° C.) and their curingstatus (level of tackiness) was monitored. A coated sample was deemedcured if the coating solidified within 5 minutes. A coated sample wasdeemed not cured if the coating did not solidify and remained tacky forat least 24 hours at room temperature. The results of the base screeningare shown in Table 1 below.

TABLE 1 Base No. Base Curing 1 DBU (1,8-Diazabicyclo[5.4.0]undec-7-ene) 

Yes 2 DBN (1,5-Diazabicyclo[4.3.0]non-5-ene)  

Yes 3 1,2-Dimethyl-1,4,5,6-tetrahydropyrimidine  

Yes 4 TBD (1,5,7-Triazabicyclo[4.4.0]dec-5-ene)  

Yes 5 MTBD (7-Methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene)  

Yes 6 2-tert-Butyl-1,1,3,3-tetramethylguanidine  

Yes 7 Phosphazene base P₁-t-Bu-tris(tetramethylene)  

Yes 8 Phosphazene base P₄-t-Bu solution (1M in Hexane)  

Yes 9 2-tert-Butylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2-diazaphosphorine  

Yes 10 2,8,9-Triisopropyl-2,5,8,9-tetraaza-1-phosphabicyclo[3,3,3]undecane  

Yes C-1 1,1,3,3-Tetramethylguanidine  

No C-2 N,N′-Diisopropylcarbodiimide  

No C-3 N,N′-Dicyclohexylcarbodiimide  

No C-4 Imidazole  

No C-5 N-Methylimidazole  

No C-6 1,2-Dimethylimidazole  

No C-7 1,4-Diazabicyclo[2.2.2]octane  

No C-8 4,4′-Trimethylenebis(1-methylpiperidine)  

No C-9 2,6-Dimethylpyridine  

No C-10 4-Dimethylaminopyridine  

No C-11 2,2,6,6-Tetramethylpiperidine  

No C-12

NoTest Method for Measuring Aced Release and Subsequent Adhesion

These tests measured the effectiveness of release liners that had beenaged for a period of time at a constant temperature and relativehumidity. The aged release value is a quantitative measure of the forcerequired to remove a flexible adhesive tape from the release liner at aspecific angle and rate of removal. This force is expressed in Newtonsper decimeter (N/dm). Unless otherwise noted, one of the following fouradhesive tapes was used to measure the aged release value and thesubsequent adhesion (sometimes called readhesion) to a substrate.

Tape I is an acrylic pressure-sensitive adhesive tape comprising apolypropylene backing commercially available from 3M Company, St. Paul,Minn. under the trade designation Scotch™ Magic™ Tape 810.

Tape II is an acrylic pressure-sensitive adhesive tape comprising apolypropylene backing commercially available from 3M Company, St. Paul,Minn. under the trade designation Scotch™ Book Tape 845.

Release liners (release-coated substrates) of the invention were testedfor their aged release values by lamination of one of theabove-described adhesive tapes, with the release coating of the releaseliner facing the adhesive-bearing side of the tape. The resultinglaminates were cut into test strips about 2.54 cm wide and approximately12 cm long. The test strips were then aged for a period of time at aconstant temperature and relative humidity (RH), as specified in thevarious examples below. The aged test strips were attached to theworking platen of a slip/peel tester (Model SP2000, obtained fromInstrumentors, Inc., Strongsville, Ohio) using a 2.54 cm widedouble-coated adhesive paper tape (commercially available from 3MCompany, St. Paul, Minn. under the trade designation 3M™ Double CoatedPaper Tape 410B) applied to the release liner side of the test strip.The attached test strip was rolled once on the working platen with a 2kg rubber roller. The adhesive tape of the test strip was then removedfrom the release liner by peeling at 180 degrees and a rate of 2.3meters per minute (90 inches per minute), and the force required forremoving the adhesive tape from the release liner was measured over afive-second data collection time.

All release tests were carried out in a facility at constant temperature(23° C.) and constant relative humidity (50 percent). At least twomeasurements were made for each example, and the data are reported as anaverage of all measurements. Measurements were made in grams-force/inchand converted to N/dm.

After peeling of the adhesive tape from the release liner, thesubsequent (180 degree peel) adhesion of the adhesive tape was measuredby adhering the freshly peeled adhesive tape (without the release liner)to a float glass test panel, with the adhesive-bearing side of the tapein contact with the panel. The adhered adhesive tape was rubbed down onthe test panel, first using light thumb pressure and then with a 2 kgrubber roller at a rate of 61 cm per minute. The subsequent adhesionvalue of the tape was then measured using the above-described instrumentand test parameters. These measurements were taken to determine whethera drop in adhesion value occurred due to undesirable contamination ofthe adhesive surface by the release coating of the release liner. Thesubsequent adhesion test was also carried out at 23° C. and 50 percentrelative humidity. At least two measurements were made for each example,and the data are reported as an average of all measurements.Measurements were made in grams-force/inch and converted to N/dm.

Example 1

A mixture of 34.0 g (0.2 mol) 1,8-diazabicylo[5.4.0]undecene and 200 mLtoluene was mixed with 34.2 g (0.2 mol) benzyl bromide. An insoluble oilformed and then changed to a white solid as the temperature rose to 57°C. over 10 minutes. After 4 hours, the solid was filtered and dried toprovide 62.5 g of 8-benzyl-1,8-diazabicyclo[5.4.0]undecane (the 8-benzylsalt of DBU, which was soluble in water). NaBH₄ solution (1.58 g, 5.1mmol, 4.4M NaBH₄ in 14M NaOH solution, obtained from Alfa Aesar, WardHill, Mass.) was diluted with 10 mL water. Then, 15 mL t-butyl methylether (t-BuOMe) was added to the diluted solution, and the resultingmixture was magnetically stirred and cooled to 3° C. To the cooledmixture was added 3.23 g of the 8-benzyl salt of DBU prepared asdescribed above. After 2 hours, the resulting cold mixture was phasesplit, the resulting aqueous layer was extracted with t-BuOMe, and theresulting t-BuOMe solutions were combined, dried, and stripped to yield0.86 g of a product (photolatent catalyst mixture). Gas-liquidchromatographic (GLC) analysis of the product indicated that itcontained 39 percent 8-benzyl-1,8-diazabicyclo[5.4.0]undecane (GLC arearesponse with a thermal conductivity detector; identified by gaschromatography/mass spectrometry (GC/MS) analysis), 13 percent ofN-3-benzylaminopropylazepine (identified by GC/MS and nuclear magneticresonance (NMR) analysis), and 48 percent of what was believed to beN-(3-benzylaminopropyl)azepin-2-one (GC/MS mass of 262).

9 g of Syl-Off™ 292 release coating composition, 0.45 g of thephotolatent catalyst mixture prepared as described above (containing 39percent 8-benzyl-1,8-diazabicyclo[5.4.0]undecane), 16.34 g heptane, 4.1g methyl ethyl ketone (MEK), and 0.11 g benzophenone were weighed into a120 mL glass jar. The glass jar was shaken until the contents werehomogeneous. The resulting homogeneous mixture was coated on the primedside of a 50 micrometers thick 3SAB PET film.

The coated film was taped to a backer board and then passed twicethrough an ultraviolet (UV) process chamber (Model MC-6RQN, availablefrom Fusion UV Systems, Inc., Gaithersburg, Md.) equipped with a 200Watts per centimeter, mercury lamp (H-bulb) at a rate of 12 meters perminute. The lamp was positioned about 15 cm above the coated film. TheUV process chamber was blanketed with nitrogen to lower the oxygenlevels. Before entering the UV process chamber, the coating on the filmwas not cured and could be smeared off when rubbed by fingers. After thefirst pass through the UV process chamber, the coating was mostly curedbut still could be scuffed off the film. After the second pass throughthe UV process chamber, the coating was cured and could not be scuffedoff with finger pressure.

Cured release liners were prepared by coating the coating solution ofExample 1 on the primed sides of 50 micrometers thick 3SAB PET films andUV-curing the coatings essentially as described above. The releaseliners were then aged for 5 days at a relative humidity of 50 percent at23° C. and 70° C., respectively. The aged release and subsequentadhesion values for the release liners were then determined by carryingout the above-described test method. The resulting data is shown inTable 2 below.

TABLE 2 Release Subsequent Subsequent Liner Release Release AdhesionAdhesion Example Laminating (N/dm) (N/dm) (N/dm) (N/dm) No. Tape (23°C.) (70° C.) (23° C.) (70° C.) 1 Tape I 0.17 0.56 36.79 23.83 1 Tape II0.26 0.57 38.62 31.60

The referenced descriptions contained in the patents, patent documents,and publications cited herein are incorporated by reference in theirentirety as if each were individually incorporated. Variousunforeseeable modifications and alterations to this invention willbecome apparent to those skilled in the art without departing from thescope and spirit of this invention. It should be understood that thisinvention is not intended to be unduly limited by the illustrativeembodiments and examples set forth herein and that such examples andembodiments are presented by way of example only, with the scope of theinvention intended to be limited only by the claims set forth herein asfollows.

We claim:
 1. A curable composition comprising (a) at least onepolydiorganosiloxane, fluorinated polydiorganosiloxane, or combinationthereof comprising reactive silane functionality comprising at least twohydroxysilyl moieties; (b) at least one polydiorganosiloxane,fluorinated polydiorganosiloxane, or combination thereof comprisingreactive silane functionality comprising at least two hydrosilylmoieties; and (c) at least one photoactivatable component that, uponexposure to radiation, generates at least one base selected fromphosphazenes, proazaphosphatranes, and combinations thereof; wherein atleast one of said components (a) and (b) has an average reactive silanefunctionality of at least three.
 2. The composition of claim 1, whereinsaid components (a) and (b) each comprise at least onepolydiorganosiloxane; wherein said polydiorganosiloxane comprisespolydimethylsiloxane; and/or wherein said component (a) ishydroxyl-endblocked.
 3. The composition of claim 1, wherein saidcomponent (a) is selected from polysiloxanes that are represented by thefollowing general formula:(OH)_(p)—Si(R′)_(3-p)-[G-Si(R′)₂]_(t)—O—[(R′)₂SiO]_(q)[Si(R′)₂-G]_(t)-Si(R′)_(3-p)-(OH)_(p)  (I)wherein each p is independently an integer of 1, 2, or 3; each G isindependently a divalent linking group; each R′ is independentlyselected from alkyl, alkenyl, fluoroalkyl, aryl, fluoroaryl, cycloalkyl,fluorocycloalkyl, heteroalkyl, heterofluoroalkyl, heteroaryl,heterofluoroaryl, heterocycloalkyl, heterofluorocycloalkyl, andcombinations thereof; q is an integer of 0 to 15,000; and each t isindependently an integer of 0 or
 1. 4. The composition of claim 3,wherein each said G is independently selected from oxy, alkylene,arylene, heteroalkylene, heteroarylene, cycloalkylene,heterocycloalkylene, and combinations thereof; each said R′ isindependently selected from alkyl, fluoroalkyl, aryl, and combinationsthereof; said q is an integer of 20 to 15,000; and/or said t is aninteger of
 0. 5. The composition of claim 1, wherein said component (a)comprises a mixture of (1) at least one polydiorganosiloxane,fluorinated polydiorganosiloxane, or combination thereof having a weightaverage molecular weight in the range of 300,000 to 1,000,000 and (2) atleast one polydiorganosiloxane, fluorinated polydiorganosiloxane, orcombination thereof having a weight average molecular weight in therange of about 150 to about 150,000; and/or wherein said component (b)has an average reactive silane functionality of at least three.
 6. Thecomposition of claim 1, wherein said component (b) is selected frompolysiloxanes that are represented by the following general formula:R′₂R″SiO(R′₂SiO)_(r)(HR′SiO)_(s)SiR″R′₂  (II) wherein each R′ isindependently selected from alkyl, alkenyl, fluoroalkyl, aryl,fluoroaryl, cycloalkyl, fluorocycloalkyl, heteroalkyl,heterofluoroalkyl, heteroaryl, heterofluoroaryl, heterocycloalkyl,heterofluorocycloalkyl, and combinations thereof; each R″ isindependently hydrogen or R′; r is an integer of 0 to 150; and s is aninteger of 2 to
 150. 7. The composition of claim 6, wherein each said R′is independently selected from alkyl, fluoroalkyl, aryl, andcombinations thereof.
 8. The composition of claim 6, wherein said R′ andsaid R″ are methyl; said r is an integer of 0; and/or said s is aninteger of
 40. 9. The composition of claim 1, wherein saidphotoactivatable component further comprises at least onephotosensitizer.
 10. The composition of claim 1, wherein saidcomposition is an organometallic catalyst-free composition; wherein saidcomposition is solventless; and/or wherein said composition has beencured.
 11. A coating process comprising (a) providing the curablepolysiloxane composition of claim 1; (b) providing at least onesubstrate having at least one major surface; (c) applying said curablepolysiloxane composition to at least a portion of at least one saidmajor surface of said substrate; and (d) inducing said curablepolysiloxane composition to cure to form a coating by exposing at leasta portion of said curable polysiloxane composition to radiation.
 12. Anarticle comprising at least one substrate having at least one majorsurface, said substrate bearing, on at least a portion of at least onesaid major surface, a coating prepared by the coating process of claim11.
 13. The article of claim 12, wherein said article further comprisesa layer of pressure-sensitive adhesive prepared by application of aphotopolymerizable composition to said coating, followed by irradiationof said photopolymerizable composition to effect photopolymerizationthereof.
 14. The composition of claim 1, wherein said base is selectedfrom (1) phosphazene compounds that are represented by the followinggeneral formula:

(2) proazaphosphatrane compounds that are represented by the followinggeneral formula:

and combinations thereof; wherein R1, R2, R3, R4, R5, R6, and R7 areeach independently selected from hydrogen, monovalent organic groups,monovalent heteroorganic groups, and combinations thereof; and whereinany two or more of R1, R2, R3, R4, R5, R6, and R7 of said phosphazenecompounds optionally can be bonded together to form a ring structure.15. The composition of claim 1, wherein said base is selected fromphosphazenes and combinations thereof.
 16. The composition of claim 15,wherein said base is selected from2-tert-butylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2-diazaphosphorine,phosphazene base P₁-t-Bu-tris(tetramethylene), phosphazene base P₄-t-Bu,and combinations thereof.
 17. The composition of claim 1, wherein saidbase is selected from proazaphosphatranes and combinations thereof. 18.The composition of claim 17, wherein said base is2,8,9-triisopropyl-2,5,8,9-tetraaza-1-phosphabicyclo[3.3.3]undecane. 19.A curable composition comprising (a) at least one polydiorganosiloxane,fluorinated polydiorganosiloxane, or combination thereof that ishydroxyl-endblocked; (b) at least one polydiorganosiloxane, fluorinatedpolydiorganosiloxane, or combination thereof comprising at least threehydrosilyl moieties; and (c) at least one photoactivatable componentthat, upon exposure to radiation, generates at least one base selectedfrom2-tert-butylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2-diazaphosphorine,phosphazene base P₁-t-Bu-tris(tetramethylene), phosphazene base P₄-t-Bu,2,8,9-triisopropyl-2,5,8,9-tetraaza-1-phosphabicyclo[3.3.3]undecane, andcombinations thereof.
 20. A curable composition comprising (a) at leastone polydiorganosiloxane, fluorinated polydiorganosiloxane, orcombination thereof comprising reactive silane functionality comprisingat least two hydroxysilyl moieties; (b) at least onepolydiorganosiloxane, fluorinated polydiorganosiloxane, or combinationthereof comprising reactive silane functionality comprising at least twohydrosilyl moieties; and (c) at least one photoactivatable componentthat, upon exposure to radiation, generates at least one base selectedfrom2-tert-butylimino-2-diethylamino-1,3-dimethylperhydro-1,3,2-diazaphosphorine,phosphazene base P₁-t-Bu-tris(tetramethylene), phosphazene base P₄-Bu,2,8,9-triisopropyl-2,5,8,9-tetraaza-1-phosphabicyclo[3.3.3]undecane, andcombinations thereof; wherein at least one of said components (a) and(b) has an average reactive silane functionality of at least three.